This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A complex problem for every eukaryotic organism is how to regulate the process of chromatin remodeling, a critical function to mediate DNA accessibility throughout the genome. Using the UCSF Mass Spec Facility, we have found that Rsc4, an essential sub unit of the RSC remodeling complex, is acetylated, by Gcn5, on K25 at its N-terminus. Purification of RSC under standard growth conditions suggests that most of Rsc4 is acetylated. In vitro comparisons of WT and mutant (K25R) RSC complexes reveal similar capabilities to remodel nucleosomes, bind DNA, and recognize acetylation. Since acetylation does not appear to alter the enzymatic properties of RSC, we are taking several in vivo approaches to understand the biological processes in which acetylation is important and to understand the functional consequences of the acetylation. Specifically, we will use mass spectrometry to identify conditions where acetylation is regulated and, combined with genetic mutations, identify the genes responsible for this regulation. These studies are the first to characterize the function of acetylation in the context of a chromatin remodeling complex.